High Efficiency Video Coding (HEVC) is a new coding standard that has been developed in recent years. In the High Efficiency Video Coding (HEVC) system, the fixed-size macroblock of H.264/AVC is replaced by a flexible block, named coding unit (CU). Pixels in the CU share the same coding parameters to improve coding efficiency. A CU may begin with a largest CU (LCU), which is also referred as coded tree unit (CTU) in HEVC. In addition to the concept of coding unit, the concept of prediction unit (PU) is also introduced in HEVC. Once the splitting of CU hierarchical tree is done, each leaf CU is further split into one or more prediction units (PUs) according to prediction type and PU partition. HEVC also supports slice structure, where a picture is partitioned into slices and each slice may use its own coding parameters or configurations.
Along with the High Efficiency Video Coding (HEVC) standard development, the development of extensions of HEVC has also started. The HEVC extensions include range extensions (RExt) which target at non-4:2:0 colour formats, such as 4:2:2 and 4:4:4, and higher bit-depths video such as 12, 14 and 16 bits per sample. One of the likely applications utilizing RExt is screen sharing, over wired- or wireless-connection. Due to specific characteristics of screen contents, coding tools have been developed and demonstrate significant gains in coding efficiency
In the current development of screen content coding for High Efficiency Video Coding (HEVC) standard, some tools have been adopted due to their improvements in coding efficiency for screen contents. For Intra blocks, Intra prediction according to the conventional approach is performed using prediction based on reconstructed pixels from neighbouring blocks. Intra prediction may select an Intra Mode from a set of Intra Modes, which include a vertical mode, horizontal mode and various angular prediction modes. For HEVC screen content coding, a new Intra coding mode, named Intra-block copy (IntraBC) has been used. The IntraBC technique that was originally proposed by Budagavi in AHG8. Video coding using Intra motion compensation, Joint Collaborative Team on Video Coding (JCT-VC) of ITU-T SG 16 WP 3 and ISO/IEC JTC 1/SC 29/WG 11, 13th Meeting: Incheon, K R, 18-26 Apr. 2013, Document: JCTVC-M0350 (hereinafter JCTVC-M0350). An example according to JCTVC-M0350 is shown in FIG. 1, where a current coding unit (CU, 110) is coded using Intra MC (motion compensation). The prediction block (120) is located from the current CU and a displacement vector (112). In this example, the search area is limited to the current CTU (coding tree unit), the left CTU and the left-left CTU. The prediction block is obtained from the already reconstructed region. Then, the displacement vector, also named block vector (BV), and residual for the current CU are coded. It is well known that the HEVC adopts CTU and CU block structure as basic units for coding video data. Each picture is divided into CTUs and each CTU is reclusively divided into CUs. During prediction phase, each CU may be divided into multiple blocks, named prediction units (PUs) for performing prediction process. After prediction residue is formed for each CU, the residue associated with each CU is divided into multiple blocks, named transform units (TUs) to apply transforms.
In JCTVC-M0350, the Intra MC is different from the motion compensation used for Inter prediction in at least the following areas:                MVs are restricted to be 1-D for Intra MC (i.e., either horizontal or vertical) while Inter prediction uses 2-D motion estimation.        Binarization is fixed length for Intra MC while Inter prediction uses exponential-Golomb.        Intra MC introduces a new syntax element to signal whether the MV is horizontal or vertical.        
Based on JCTVC-M0350, some modifications are disclosed by Pang, et al. in Non-RCE3: Intra Motion Compensation with 2-D MVs, Joint Collaborative Team on Video Coding (JCT-VC) of ITU-T SG 16 WP 3 and ISO/IEC JTC 1/SC 29/WG 11, 14th Meeting: Vienna, A T, 25 Jul.-2 Aug. 2013, Document: JCTVC-N0256 (hereinafter JCTVC-N0256). Firstly, the Intra MC is extended to support 2-D MVs, so that both MV components can be non-zero at the same time. This provides more flexibility to Intra MC than the original approach, where the MV is restricted to be strictly horizontal or vertical.
In JCTVC-T1005 (Joshi, et al., HEVC Screen Content Coding Draft Text 3, Joint Collaborative Team on Video Coding (JCT-VC) of ITU-T SG 16 WP 3 and ISO/IEC JTC 1/SC 29/WG 11, 20th Meeting: Geneva, C H, 10-18 Feb. 2015, Document: JCTVC-T1005), the Intra block copy mode is harmonized with normal Inter mode. The reconstructed current picture before deblocking is inserted to the List 0 reference frame list as one of the reference frame. The Intra block copy mode is signalled by setting refldx (i.e., reference picture index) to point to the reconstructed current picture. Therefore, for a current picture, two pictures are required to be output. One is the un-filtered picture (i.e., before deblocking), and the other is the filtered picture (i.e., after sample adaptive offset, SAO). In order to support the Intra block copy, the worst case bandwidth (BW) of screen content coding (SCC) is larger than HEVC and HEVC ReExt.
In JCTVC-T0045 (Lainema, et al., AHG10: Memory bandwidth reduction for intra block copy, Joint Collaborative Team on Video Coding (JCT-VC) of ITU-T SG 16 WP 3 and ISO/IEC JTC 1/SC 29/WG 11, 20th Meeting: Geneva, CH, 10-18 Feb. 2015, Document: JCTVC-T0045) and JCTVC-T0051 (Laroche, et al., AHG10: On IBC memory reduction, Joint Collaborative Team on Video Coding (JCT-VC) of ITU-T SG 16 WP 3 and ISO/IEC JTC 1/SC 29/WG 11, 20th Meeting: Geneva, C H, 10-18 Feb. 2015, Document: JCTVC-T0051), a method is disclosed to signal a CTU-level flag to indicate whether the current CTU will be referred by the following blocks for Intra block copy mode. If the flag is 1, the deblocking and SAO of this CTU are disabled. This CTU can be used for Intra block copy mode. Otherwise, the deblocking and SAO are enabled for this CTU. In this case, the CTU cannot be used for Intra block copy mode for the following blocks. Therefore, only one kind of CTU needs to be output. The worst case bandwidth is the same as HEVC.
Since the reference pictures are usually stored in DRAM (dynamic random access memory), the memory bandwidth calculation needs to take the DRAM data access behaviour into account. For the bandwidth estimation, equation (1) is usually used to calculate the average number of pixels that are required for the interpolation of each pixel in the worst case. The M and N are the PU width and height, m and n are width and height of a memory unit of one address in DRAM. If bi-prediction is used, this number should be doubled.
                    P        =                                            ⌈                                                m                  -                  1                  +                  M                  +                  L                  -                  1                                m                            ⌉                        ×                          ⌈                                                n                  -                  1                  +                  N                  +                  L                  -                  1                                n                            ⌉                        ×            m            ×            n                                M            ×            N                                              (        1        )            
In the above equation, “┌x┐” represents a ceiling function corresponding to the smallest integer not less than x.